1. Field of the Invention
The invention relates generally to a mechanism for dispensing medicament via an outlet nozzle, and relates more particularly to a one-way actuation release mechanism for a medicament dispensing system for applying medicament from a vial-dispenser of the type which is actuated by compression or movement of a trigger.
2. Description of Related Art
Amongst various dispensers for applying medicament, a typical medicament container includes a flexible vial storage portion and a nozzle for dispensing medicament by squeezing the vial between its side walls. Another type of medicament dispenser is an accordion-like or piston-like dispenser which is actuated by squeezing the vial between a bottom wall and the nozzle so as to compress the vial in its longitudinal direction, rather than from its sides. The present invention is particularly directed to a dispensing system which includes such an accordion-like or piston-like dispenser, although the present invention may be used in conjunction with other types of dispensers. An example of the piston-like dispenser which ejects precalibrated dosage of medicament is described in detail in my U.S. Pat. No. 5,613,957 which is expressly incorporated herein by reference.
Normally, several factors contribute to difficulty in applying medicament. First, elderly people often encounter difficulty in holding the dispenser steady or squeezing the dispenser to apply a proper quantity of medicament. In addition, even for young persons who are able to hold the dispenser steady, actuation of certain types of dispensers creates problems in accurate application of medicament. For example, application of medicament using a common type of nasal dispenser requires initial placement of the nozzle tip inside the nostril, followed by withdrawal of the nozzle tip from the nostril due to the compression of the dispenser at the time of ejection of medicament, which may result in accidental application of medicament to the eyes or other unintended targets.
Even if the medicament is properly applied as intended, typically the dispensed dose of medicament will vary with the speed and/or the force of actuation of the pump mechanism. In addition, the spray pattern, or the plume, of the dispensed medicament will also vary with the speed and/or the force of actuation of the pump mechanism.
Yet another problem associated with medicament dispensers is manufacturing complexity: pump-type medicament dispensers are currently made of numerous parts and are highly delicate to assemble. Many of the pump-type dispensers incorporate springs, which pose problems in the manufacturing process for the dispensers because of the springs' tendency to get intermingled.
One attempt to solve the above-described problems associated with applying medicament from a dispenser is described in my U.S. Pat. No. 5,267,986, which discloses a system including a cartridge for actuating a piston-like or accordion-like vial-dispenser for applying medicament to an eye. The cartridge disclosed in U.S. Pat. No. 5,267,986 includes: a housing for holding the vial-dispenser; a telescoping cylinder for compressing the vial-dispenser in the longitudinal direction to load the vial with medicament; a locking mechanism for locking the telescoping cylinder and the vial-dispenser in the loaded position, against the urging of a spring mechanism of the vial-dispenser; and a trigger mechanism for releasing the telescoping cylinder and the vial-dispenser from the locked position to release the medicament loaded in the dispenser by means of the force of the spring mechanism. In order to obviate the need for a discrete spring element in the pump mechanism of the vial-dispenser, a portion of the vial-dispenser body is made of an elastic material which is compressible and provides spring force. The two-step process in which the cartridge disclosed in U.S. Pat. No. 5,267,986 loads and subsequently releases the medicament from a vial-dispenser defines the basic operation a "reverse pump," an example of which is described in U.S. Pat. No. 5,613,957.
The dispensing system disclosed in U.S. Pat. No. 5,267,986 addresses the previously-mentioned problems by enabling a user to apply a predetermined dose of medicament independent of the physical force applied to the dispensing system by the user: the releasing force or speed of the dispensed medicament is dependent on the integral spring element of the dispensing system. Whereas conventional pump-type dispensers often utilize compression along the longitudinal axis for release of medicament, the actuation motion of the release mechanism described in U.S. Pat. No. 5,267,986 is preferably achieved in a direction perpendicular to the longitudinal axis of the vial-dispenser to ensure enhanced leverage for the user.
Because elastic materials, particularly elastomeric materials and springs, tend to exhibit hysteresis, spring force decreases if the spring mechanism is kept in the compressed position, i.e., in the loaded, locked position. Although the deformation of spring is generally reversible if the spring is returned to, and maintained in, the unbiased state for some period, some of the deformation becomes irreversible, or experiences "creep," if the spring is kept in the compressed state beyond a certain threshold period of time, which threshold period varies with the spring material. The amount of loss of spring force is dependent on the tendency of a particular spring material to "creep," and it is known that metal springs tend to exhibit much less "creep," than plastic springs. The hysteresis of elastic materials used to form the spring mechanism of the pump described in U.S. Pat. 5,613,957 is due to loss of some of the spring property when the spring element remains in the compressed state for an extended period of time.
Two examples illustrate the practical implications of the above-mentioned hysteresis problem-in connection with the dispensing system disclosed in U.S. Pat. No. 5,267,986. As a first example, a user places the dispensing system in the loaded state but does not actuate the release mechanism for several minutes due to an interruption. When the release mechanism is finally actuated, hysteresis of the spring mechanism causes the dosage of released medicament to vary from the dosage calibrated to be released under normal conditions. As a second example, a user places the dispensing system in the loaded state but subsequently forgets about the loaded system; the user does not actuate the release mechanism for several weeks or months. In this situation, not only will the initially-released dosage vary from the calibrated dosage, but subsequently-dispensed dosages will also vary from the calibrated dosage due to a type of permanent deformation, or "creep," that has occurred.
In view of the above-described problem of spring deformation, it would be desirable to have a medicament-dispensing system which allows the user, by means of a single actuation motion, to load the vial with medicament and dispense the medicament.